Where did “Bob’s your uncle” originate from?

There are three ideas where it could come from - the favourite origin is:
1. Bob's your uncle - Arthur Balfour'Bob's your uncle' is often said to derive from the supposed nepotism of Lord Salisbury, who appointed a favourite nephew, Arthur Balfour, to several political posts in the 1880s. Balfour went on to become Prime Minister after his uncle, but his early political appointments were considered inappropriate as he had shown no prior interest in public work. It is unlikely that Arthur Balfour would ever have become a celebrated politician without the patronage of his influential uncle. Piers Brendon, in Eminent Edwardians, 1979, writes:
"In 1887, Balfour was unexpectedly promoted to the vital front line post of Chief Secretary for Ireland by his uncle Robert, Lord Salisbury."
The link here between an uncle Bob who was Prime Minister and a 'Bob's your uncle' passport to a cushy life is easy to make.The fact that the word 'nepotism' derives from 'nephew' makes the link seem all the more neat. Such neatness is often the mark of a back-formation, that is, an explanation that is made up after the event.
2. A second interpretation has it that the phrase derives from the slang term 'all is bob', meaning 'all is well'. That term is listed in Captain Francis Grose’s Dictionary of the Vulgar Tongue, 1785:
A shoplifter’s assistant, or one that receives and carries off stolen goods. All is bob; all is safe.
The slang word 'bob', meaning 'shoplifter's assistant', had been in circulation for some years at that time and is defined as such in Nathan Bailey's Dictionary of Canting and Thieving Slang, 1721. More generally, 'bob' was used as a generic name for 'person', like 'Jack', 'Jill', 'Joe' etc. For example, public schoolboys who indulged in land sports like cricket or rugby were called 'dry bobs' and those who preferred boating were called 'wet bobs'.
3. The third potential source is the music hall. The earliest known example of the phrase in print is in the bill for a performance of a musical revue in Dundee called Bob's Your Uncle, which appeared in the Scottish newspaper The Angus Evening Telegraph in June 1924.
Bob's your uncleThe expression also formed part of the lyrics of a song written by John P. Long, and published in 1931 - Follow Your Uncle Bob. The lyrics include:
Bob's your uncle
Follow your Uncle Bob
He knows what to do
He'll look after you
The song was sung and recorded by Florrie Forde, the celebrated music hall artiste of the early 20th century.
Eric Partridge lists it in A Dictionary of Slang and Unconventional English, 1937. He states it as dating from circa 1890, although he presents no evidence for that.
The difficulty with the first two suggested origins is the date. The phrase itself isn't recorded until the 1920s. It would seem odd for a phrase to be coined about the nepotism of an uncle for his nephew well after both Prime Ministers were out of office. The 'all is bob' origin is from a century or so earlier and appears to have little reason to be connected to 'Bob's your uncle' other than that they both contain the word 'bob'.
This isn't the first time that an etymological outsider romps home when the favourites have fallen at the first fence. We don't know for sure but, based on current knowledge, this classically English expression may well prove to be Scottish and derive not from 10 Downing Street but from the King's Theatre, Dundee